1. Field of the Invention
The present invention relates to a solenoid operated valve for permitting or interrupting the flow of hydraulic fluid passing therethrough, and more particularly to a solenoid operated valve adapted for use in a skid-control apparatus, a traction control apparatus or the like in a braking system of an automotive vehicle.
2. Description of the Prior Art
Disclosed in Japanese Patent Laid-open Publication No. 4(1992)-266676 is a solenoid operated valve of this kind which includes a valve housing formed with a valve chamber, an end closed sleeve concentrically assembled within the solenoid winding and having an opening end mounted on the valve housing, a stationary element mounted within the end closed sleeve, a movable element axially movably mounted within an closed end portion of the sleeve to be moved toward the stationary element against a return spring loaded thereto when the solenoid winding is energized, a movable valve rod concentrically assembled within the stationary element for movement with the movable element, a valve body integrally provided with a distal end of the movable valve rod and located in the valve chamber, a valve seat mounted within the valve chamber and having a valve hole to be closed by the valve body, and a hydraulic damping mechanism for restraining movement of the valve body in operation of the solenoid operated valve. In the solenoid operated valve, the damping mechanism is designed to reduce mechanical noises in operation of the solenoid operated valve and to restrain sudden restriction or expansion of a fluid passage formed between the valve seat and valve body.
In the solenoid operated valve, the return spring is disposed between the valve body and the valve seat, a check valve with a throttle acting as a hydraulic damper is disposed within a cylinder portion formed in the stationary element in surrounding relationship with the movable valve rod, and an orifice is formed by a portion of the valve hole. The check valve is assembled with the movable valve rod for permitting the flow of hydraulic fluid into a damper chamber formed between the movable valve rod and the cylinder portion of the stationary element and associated with an annular throttle passage formed between a ring disc of the check valve and the cylinder portion of the stationary element or an orifice formed in the cylinder portion of the stationary element.
In the solenoid operated valve, sufficient damping function may not be effected for the following reasons.
1) A sufficient displacement capacity of the damper chamber may not be obtained during movement of the valve body. PA1 2) The damping function of the check valve is effected only when the valve body is moved in one direction. PA1 3) The orifice formed in the valve hole acts to throttle the flow of hydraulic fluid only at an initial stage of closing operation of the valve body and also at the last stage of opening operation of the valve body. This means that the damping function is effected only in a condition where the opening area of the fluid passage formed between the valve body and valve seat becomes less than the opening area of the orifice. In other words, the damping function is effected only by a portion of the entire movement amount of the valve body.